The present invention relates to a lifting element for a rotary mill consisting of a parallelepipedal block of elastomer designed to be fixed to the internal wall of a rotary grinder containing grinding implements and to form part of the lining of the latter. The invention also relates to a rotary mill comprising a cylindrical shell the internal lining of which includes such lifters.
The invention more particularly relates to the field of mills which are run wet, particularly those used in cement making or in the mining industry for crushing and grinding minerals. These mills consist of a cylindrical shell rotating about its longitudinal axis and containing a grinding charge consisting of grinding implements such as balls, cylpebs, boulpebs, etc. of different sizes.
The shell includes an internal lining consisting of lining plates and of what are called lifting elements or lifters having the function of mixing and entraining the grinding charge and the material to be ground. The latter is introduced on one side of the mill and, as it progresses towards the outlet, on the opposite side, it is ground and crushed between the grinding implements.
Given that the grinding takes place progressively in the direction of throughput through the mill, the best grinding conditions are achieved when the size of the grinding implements is matched to that of the material to be ground. In other words, the coarsest grinding implements should, preferably, be concentrated on the inlet side of the mill, whereas the smallest ones should be located on the outlet side. This is what is known as the classification of the grinding implements as a function of their size. Under optimum conditions, this classification should therefore be achieved automatically during the operation of the mill.
Moreover, in the interest of effectiveness of the grinding and the durability of the grinding implements, it is necessary, as far as possible, to avoid projections and drops of the latter in favour of intense sliding and intense mixing, which are favourable to the crushing and grinding of the material between the moving grinding implements.
To date, the linings of the mills running wet were either made from cast iron or from alloy steels, or from elastomer. The linings made from cast iron or alloy steels have the drawback of a high weight and time-consuming manipulation when installing the elements forming the lining. Furthermore, they are extremely noisy and no longer respond to the ever increasingly severe environment criteria.
To resist wear, the elastomer linings had lifting elements which were bigger than those of the metallic linings. These thicker and more projecting elements still tend to project the grinding bodies when the mill rotates. Now, the projection of the grinding implements reduces the effectiveness of the grinding and accelerates the wear of the grinding implements by cracking and micro-splintering.
Furthermore, it has been noted that thick and projecting elastomer lifting elements tend to give rise to a longitudinal segregation of the grinding implements which is contrary to the envisaged classification, so that the small grinding implements are often found at the inlet to the mill and the coarser ones are often found on the outlet side, whereas, for effective grinding, it is the contrary which is envisaged.